The present invention relates to an automatic document feeder associated with a facsimile apparatus, a copier or like machine for automatically feeding a desired number of documents one by one to a predetermined station inside the machine.
In one type of facsimile apparatuses and others known in the art, a stationary document reader scans a document which is moved along a predetermined path so as to focus the resulting optical data onto a photoelectric transducer, i.e. a charge coupled device (CCD). Document feed in this type of apparatus is generally implemented with a relatively simple automatic document feeder (ADF). A prior art ADF for such an application includes a separator roller and a flat friction member which is pressed against the separator roller, so that documents stacked on a tray are separated one at a time based on the differences in friction between the separator roller, friction member and documents. This prior art ADF, however, is operable only under limited separation conditions partly because the pressure force exerted by the friction member and the coefficient of friction of documents are not always constant. In addition, where a single document is to be fed by such an ADF, the document and the friction member are apt to slip on each other resulting in skew feed or delayed feed of the document. Another prior art ADF which is designed to eliminate the above drawbacks uses a roller in place of the flat friction member and maintains the roller (hereinafter referred to as a document stop roller) in pressing contact with the separator roller. In this kind of prior art ADF, a relationship that the coefficient of friction between documents is greater than that between the document stop roller and the documents which in turn is greater than that between the documents is set up, allowing a stack of documents to be fed sequentially one by one from the bottom of the stack. Where a single document is to be fed, the document stop roller which is in a free state is rotated by the separator roller to successfully deliver the document. However, just as it solves the problems particular to the previously stated flat friction member scheme, it brings about another problem that a solenoid, a clutch and other special mechanisms are needed to prevent two or more documents from being fed continuously and, also, additional rollers for positively driving a separated document are essential, the resulting ADF being bulky and disproportionate in the number of structural elements.